Computer systems often require linkages between applications such as those found in process control systems used to control oil refineries. So, for example, an operator at a graphical workstation could select a graphic symbol indicative of a valve, and change its status from closed to open to affect a change to its image on the display and a corresponding change to the process environment where the valve is closed. However, most process control systems were "hard-coded" to perform specific tasks. The linkages were not easily redefined via an operator's console. Further, the linkages were not flexible or multi-purpose. Rather each linkage had a predefined task that could not be readily changed.
More recently, Apple and other interactive computer systems have provided linkages between closed documents and containers or folders. So, for example, a user of an interactive computer system could select a graphical symbol indicative of a document and open the document via the graphical symbol. A folder could have a selected document dropped into it via the graphical symbol indicative of the folder.